Pergola Installation

Here are a few photos of the pergola structure, sans pv panels. Powerfully Green built it out of cedar with massive 6x6 posts. Because we're a duplex we have a 9' setback from the property lines. We could have done an additional 3 panels if we had another four feet. Generally the setback is 6' in St. Paul, MN. We love the pergola idea because we have so little roof space. They will squeeze in 9 panels on the roof, but that will leave no space for solar water or additional panels.

The trench! They dug down about 24." They managed to get it dug and filled before the ground got too frozen. I'm glad I didn't have to dig this trench. The black box under the pergola is a compost bin. We'll move it in the spring; we intend to use the space under the panels for bike and scooter parking.

kWh Consumption and Production

The Metroplex, a 1922 up-down duplex, has two Xcel energy accounts, that is two power lines in, two meters. For a variety of reasons, we're going to tie into the upper unit's feed, but are internally combining the billing since we share in the consumption in both units.

The lower unit uses more electricity because as a whole household we have three compressors running (freezer, fridge, and basement dehumidifier), and often a heater in the chicken coop. The upper unit has only one compressor on its circuits. We have no air conditioning.

We have windows in every room so for a lot of the year our lighting needs are met by the sun. For example, right now, in our unit we have a computer running (this one) and not a whole lot more. It's sunny out and we really don't need additional light anywhere. Upstairs we've been working on eliminating "phantom-load" and have been reluctant to purchase electronic equipment or appliances that rely on standby power.

For the upper unit our last year consumption in kWh was this:
10/24/10 - 169 kWh
9/23/10 - 208 kWh
8/24/10 - 162 kWh
7/26/10 - 160 kWh
6/24/10 - 162 kWh
5/25/10 - 147 kWh
4/26/10 - 136 kWh
3/28/10 - 209 kWh
2/25/10 - 369 kWh
1/27/10 - 479 kWh
12/28/09 - 275 kWh
11/23/09 - 192 kWh

Average: 222 kWh

Lower unit:
10/24/10 - 270 kWh
9/23/10 - 343 kWh
8/24/10 - 547 kWh
7/26/10 - 625 kWh
6/24/10 - 379 kWh
5/25/10 - 427 kWh
4/26/10 - 356 kWh
3/28/10 - 350 kWh
2/25/10 - 310 kWh
1/27/10 - 661 kWh
12/28/09 - 428 kWh
11/23/09 - 317 kWh

 Average: 418 kWh

Total metroplex monthly consumption: 640kWh.

Our system will be 3.24 kW composed of 18 Silicon Energy 180 watt modules with 9 modules flush mounted on house roof and 9 mounted on pergola in yard.

By the estimates from the National Renewable Energy Laboratory (NREL)

Month	Solar Radiation (kWh/m2/day)	AC Energy (kWh)	Energy Value ($)
1	3.85	325	25.68
2	4.72	348	27.49
3	4.97	393	31.05
4	4.90	353	27.89
5	5.73	410	32.39
6	5.91	398	31.44
7	5.88	409	32.31
8	5.64	393	31.05
9	5.21	362	28.60
10	4.28	320	25.28
11	2.95	220	17.38
12	2.85	234	18.49
Year	4.74	4165	329.04

On a monthly average, our system hopefully will produce ~345kWh. Or approximately 54% of our use.

The fanatic in me wonders, so what else can we reduce? I'd love to see the dial spin backwards and have Xcel pay us.

Photo Voltaic Intertie System Part 1

Sometime in the early part of 2010 I was doing research on how to build a solar electric back up for our pellet stove. As I researched it, I found that it was going to be fairly expensive to do well. Along the way, I also uncovered the state, federal and utility incentives to installing an inter-tie system. Once I understood how much of the system (about 70%) would be paid for through incentives, the decision seemed already made.

After several campaigns to reduce our energy consumption in the metroplex, our electrical consumption was down to about 420KWH for the lower unit and 165KWH for the upper unit.

About three years ago we had investigated solar hot water heat, but had a very bad experience with a local contractor who took over a month to do the site assessment and then refused to return our phone calls with questions about the quote and the system he was proposing. Other things got in the way, and we just let the project drop.

Several of our friends had used Rebecca Lundberg at Powerfully Green  for installations and were very happy with her work. We have been absolutely thrilled with her and her partner Dan Williams. They have answered all our crazy questions, and been incredibly resourceful, committed, helpful and creative in dealing with our installation. I cannot recommend their team high enough.

We were originally considering a roof-only installation which would have been considerably smaller (about half) than the 3.24KW system we are installing.We also considered build an "awning" off of the back deck, but decided against it because it would have been ugly and shaded key garden beds.

As we worked through design options, we had heard that the state was about to close applications because the money was running out. Rebecca and Dan submitted the paperwork for the state rebate, and we began the waiting phase. Without the state rebate it would have been difficult and significantly more costly to install; the project would probably have been called off without that rebate.


Powerfully Green came through with an excellent proposal: to double the potential of the system by building a backyard pergola. Rebecca and Dan had just installed a pergola with good success. After reviewing their proposal, we decided to go for the larger system with the pergola.

So our 3.24 kW system will be 18 Silicon Energy 180 watt modules with 9 modules flush mounted on house roof and 9 mounted on pergola in yard. We'll have a Power One 4.2 inverter. In addition to building the Pergola, they will be switching out our old fuse-based AC main panel and replacing it with a breaker style system.

Silicon Energy's modules are manufactured in Washington State, and will soon be made in Minnesota!

Total installed cost including all permits: $34,995.00

less 30% federal tax credit $10,498.50
less Minnesota State Solar-Electric Rebate of $5,670.00
less  Xcel Energy rebate of $7,290.00

= $11,036.50 net cost

This will be a little higher because we are installing an outside outlet on the pergola for charging our eGo electric bike, and adding a TED monitor. 

Photos coming soon!